> On 20 Mar 2025, at 22:19, Thiago Macieira <thiago_at_[hidden]> wrote:
>
> On Thursday, 20 March 2025 10:08:57 Pacific Daylight Time Hans Åberg wrote:
>>> But the C++ feature should not rely on developers using pragma, because
>>> the
>>> specific pragmas are not part of the standard. The feature must assume
>>> that all warnings will be dealt with as "this must be fixed" and
>>> developers will just change the code.
>>
>> If they decide compile that way, it is their business, not of the standard.
>> The standard does not specify to issue warnings in the compile, only giving
>> some cases where it might be appropriate.
>
> Which means a perfectly-compliant compiler may issue no warning on the use of
> [[unimplemented]]. What's the difference between that and having no attribute?

The standard has no control over what compiler writers will do.

>>> That means this feature's only remaining use is that an [[unimplemented]]
>>> declaration can later be overridden as implemented. You'll need to explain
>>> why this can't simply be done by changing the first declaration and how
>>> that is not fragile in the first place. What happens if the declaration
>>> order changes?
>>
>> The same. But if used in a standard library, the order will not change.
>
> The most common use will not the in the Standard Library. Please design it
> with the most common use-case in mind.

The intended design is for use in the standard library.

>>> If it's a temporary thing, I can name my function however I want.
>>
>> Indeed, but the guy who wrote it leaves, and later when the implementation
>> is added, others will have to figure how to fix it instead of doing more
>> important things. A similar question arose on a 600 k lines of C++ code
>> project.
>
> And fixing [[unimplemented]] is still work. If the original party adds the
> function, now we have two definitions and the linking may fail (ODR violations
> are IFNDR) - it will fail if linking statically.

There is no work needed; the workaround implementation will be not called, and its single occurrence can be removed at some point.